How much bacteriostatic water do I add to a 5 mg oxytocin vial?

There is no single right amount. More water makes each draw bigger and easier to measure; less water keeps the volume small. With 2 mL, a 5 mg vial is 2.5 mg/mL, so every 10 units on a U-100 insulin syringe holds 250 mcg. With 1 mL it is 5 mg/mL (500 mcg per 10 units). With 3 mL it is 1.67 mg/mL (166.667 mcg per 10 units). With 5 mL it is 1 mg/mL (100 mcg per 10 units).

How many units is 100 mcg of oxytocin from a 5 mg vial?

With 2 mL of water the vial is 2.5 mg/mL, so 100 mcg is 0.04 mL, or 4 units on a U-100 syringe. With a different water volume the units change but the amount does not. The amount is an example for the math, not a recommendation.

How many 100 mcg draws are in a 5 mg oxytocin vial?

50 (5 mg ÷ 100 mcg), whatever volume of water you add. In practice a little is lost to the syringe dead space and the last drops in the vial.

Oxytocin 5 mg Reconstitution: BAC Water & Units

Short answer: 2 mL of bacteriostatic water in a 5 mg oxytocin vial makes 2.5 mg/mL. On a U-100 insulin syringe (1 mL = 100 units), every 10 units then holds 250 mcg. More water gives a weaker solution and a bigger draw for the same amount; the amount in the vial stays 5 mg.

Water volume chart for a 5 mg vial

5 mg oxytocin vial, U-100 insulin syringe.
Water added	Concentration	Per 10 units	Per 1 unit
1 mL	5 mg/mL	500 mcg	50 mcg
2 mL	2.5 mg/mL	250 mcg	25 mcg
3 mL	1.67 mg/mL	166.667 mcg	16.667 mcg
5 mL	1 mg/mL	100 mcg	10 mcg

Syringe units by amount

The amounts below are examples to show the conversion, not doses. How much to take is a decision for you and your prescriber.

Units on a U-100 syringe from a 5 mg vial.
Water added	50 mcg	100 mcg	200 mcg
1 mL	under 2 units	2 units	4 units
2 mL	2 units	4 units	8 units
3 mL	3 units	6 units	12 units
5 mL	5 units	10 units	20 units

A 5 mg vial holds 100 draws of 50 mcg, 50 draws of 100 mcg, 25 draws of 200 mcg, no matter how much water you add.

How far a 5 mg vial goes

Draws per vial depend only on the amount per draw, not on the water. The volume and units columns use 2 mL of water (2.5 mg/mL). Example amounts only, not doses.

5 mg vial: draws, volume and units per example amount.
Amount per draw	Draws per vial	Volume per draw	Units per draw
25 mcg	200	0.01 mL	under 2 units
50 mcg	100	0.02 mL	2 units
100 mcg	50	0.04 mL	4 units
200 mcg	25	0.08 mL	8 units
400 mcg	12.5	0.16 mL	16 units

Real counts run a little lower: some liquid stays in the syringe and at the bottom of the vial.

5 mg next to other oxytocin vial sizes

To get the same 2.5 mg/mL from another vial size, scale the water with the vial. Same strength means the same units for the same amount, whichever vial it comes from.

Water for 2.5 mg/mL, and 100 mcg draws per vial, by vial size.
Vial	Water for 2.5 mg/mL	100 mcg draws per vial
2 mg	0.8 mL	20
5 mg (this page)	2 mL	50

The math

Concentration. 5 mg ÷ 2 mL = 2.5 mg/mL
Volume to draw. amount ÷ 2.5 mg/mL = mL
Syringe units. mL × 100 = units

For a different water volume or amount, the free peptide reconstitution calculator works backwards from the amount you want and suggests a water volume that lands on a clean syringe mark.

Other oxytocin vial sizes: Oxytocin 2 mg

Half-life, time to peak and sources are on the main Oxytocin guide.

Oxytocin 5 mg reconstitution: how much water and how many units